This invention relates to an electronic driver circuit for controlling the operation of a solenoid having at least two coils and more particularly to controlling the operation of a fuel injector for a diesel engine.
Prior driver circuits previously utilized for the control of diesel fuel injectors have been large and have displayed power dissipation which is excessive. The most difficult aspect of developing a driver which meets the need of diesel injectors, that have large flow capacity, is the high power and high voltage required for rapid operation. To achieve rapid response and to minimize the delay and motion time of the solenoid movement many driver circuits have used a capacitive boost circuit which contributes to the driver circuits large size and high costs.
By utilizing a solenoid having two coils, the present driver reduces heat dissipation. The present invention provides a fast and repeatable response and displays reduced power and size requirements.
As described in detailed below, the invention is directed to a driver circuit for a solenoid actuated fuel injection valve which uses a single solenoid having two coils, a first or pull-in coil to open the injector valve and a second or hold coil to maintain the movable plunger of the solenoid in an open position. In response to pulse width signals generated by an electronic control unit or ECU, a boost current pulse is supplied to the driver coil for opening the injector valve. The boost current is not regulated during the boost mode, however, the duration or pulse width of the boost current pulse is controlled as a function of the battery voltage in order to compensate for variations in battery voltage.
An advantage of the present system is that it is capable of operating at battery voltages as low as 5.3 volts. In addition, the driver contains circuitry which controls the undershoot or current droop which is inherent in solenoid driver circuits having boost and hold modes of operation and includes circuitry to inhibit solenoid operation when the input metering pulse transmitted from an electronic control unit is ill conditioned.
Many other features and advantages of the present invention will be clear from the following detailed description of drawings.